Thorium can be used as an alternative nuclear fuel. However natural thorium (thorium-232) has no fissile isotope, so in the early stages of burning should be added fissile nuclides such as Plutonium-239. This study presents the results of a parameter study of calculation thorium-based fuel cells with or without addition of plutonium-239. The volume fraction of cells used is 65% fuel, 10% stainless steel as a cladding and 25% helium as the coolant. Neutronic parameters calculated was the effective multiplication factor (keff), infinite multiplication factor (kinf) and nuclide density changes as the result from the fission nuclides over time burnup fuel. Those parameters indicated the influence of plutonium-239 addition to the level of critical reactor.